This invention relates to stain-resistant, dyeable sheath/core filaments and methods. More particularly, this invention relates to sheath/core filaments wherein the core component is susceptible to dyeing by dye chemicals in a dye bath, while the sheath component is resistant to dyeing by such dye chemicals in the dye bath.
As used herein, xe2x80x9cdyedxe2x80x9d refers to the results of an intentional coloration process performed by exhaust or continuous dyeing methods that are known in the art after the material (i.e., fiber) is extruded by incorporating one or more colored chemical compositions into the material at elevated temperature. In contrast, the term xe2x80x9cstainedxe2x80x9d means the discoloration of fibers caused by the binding of a colored material either ionically, covalently, or through chemical partitioning to the fiber. The term xe2x80x9cstain resistantxe2x80x9d and xe2x80x9cstain resistancexe2x80x9d as used herein with respect to polyamide fibers or carpets refers to the ability of the fiber or carpet to resist red drink and/or coffee stains. xe2x80x9cInherently chemically compatiblexe2x80x9d means that the materials referred to are miscible.
Polyamide fibers are relatively inexpensive and offer a combination of desirable qualities such as comfort, warmth and ease of manufacture into a broad range of colors, patterns and textures. As a result, polyamide fibers are widely used in a variety of household and commercial articles, including, e.g., carpets, drapery material, upholstery and clothing. Carpets made from polyamide fibers are a popular floor covering for both residential and commercial applications.
Polyamide fibers tend to be easily permanently stained by certain natural and artificial colorants such as those found in such common household beverages as coffee, wine and soft drinks. Such household beverages may contain a variety of colored anionic compounds including acid dyes, such as the red dyes used in children""s drinks. The stains resulting from such compounds cannot easily be removed under ordinary cleaning conditions.
The ability of a staining material like an acid dye to bind to a fiber is a function of the type of active functional groups on the fiber and of the staining material. For example, polyamides usually have terminal (often protonated) amine groups which bond with negatively charged active groups on an acid dye (or staining agent).
A commonly used acid dye colorant and one which severely stains nylon at room temperature is Color Index (xe2x80x9cC.I.xe2x80x9d) Food Red 17, also known as FDandC Red Dye 40. Acid dyes such as C.I. Food Red 17 often form strong ionic bonds with the protonated terminal amine groups in the polyamide polymers, thereby dyeing, i.e., staining, the fiber. Thus, in contrast to soils which are capable of being physically removed from the polyamide carpet by typical cleaning procedures, acid dye colorants such as C.I. Food Red 17 penetrate and chemically react with the polyamide to form bonds therewith which make complete removal of such colorants from the polyamide fibers impractical or impossible.
The exact mechanism of coffee as a staining agent is not well understood. However, as with acid dye stains, coffee stains are notoriously difficult to remove from polyamide carpet by conventional cleaning procedures.
This severe staining of carpeting is a major problem for consumers. In fact, surveys show that more carpets are replaced due to staining than due to wear. Accordingly, it is desirable to provide polyamide fibers which resist common household stains like red drink and coffee stains, thereby increasing the life of the carpet.
Methods to decrease the acid dye affinity of nylons by reducing the number of dye sites are known. For example, U.S. Pat. No. 3,328,341 to Corbin, et al. describes decreasing nylon dyeability with butrylactone. U.S. Pat. No. 3,846,507 to Thomm et al. describes reducing acid dye affinity of polyamide by blending a polyamide with a polymer having benzene sulfonate functionality. U.S. Pat. No. 5,108,684 to Anton et al. describes fibers made from polyamide copolymers containing 0.25 to 4.0 percent by weight of an aromatic sulfonate, which are stain-resistant to acid dyes. U.S. Pat. No. 5,340,886, Hoyt et al. describes acid dye resistant polyamide fibers made by incorporating within the polymer sufficient SO3H groups or salts thereof to give the polymer a sulfur content of between about 1 and about 160 equivalents per 106 grams polymer and, chemically blocking with a chemical blocking agent a portion of amine end groups present in the sulfonated polymer. Modified polymers such as described in these patents are generally expensive to make.
In addition to polymer modifications, topical treatments for carpets have been proposed as a cost effective means to impart acid dye resistance to polyamide carpet fibers. These topical treatments may be sulfonated materials that act as xe2x80x9ccolorless dyesxe2x80x9d and bind the amine dye sites on the polyamide polymer. Sulfonated products for topical application to polyamide substrates are described in, for example, U.S. Pat. No. 4,963,409 to Liss et al.; U.S. Pat. No. 5,223,340 to Moss, III, et al.; U.S. Pat. No. 5,316,850 to Sargent et al.; and U.S. Pat. No. 5,436,049 to Hu. (Hu describes also a polyamide substrate that is made by melt mixing a polyamide with an amine end group reducing compound prior to fiber formation.) Topical treatments tend to be non-permanent and to wash away with one or more shampooings of the carpet.
Fibers may be formed in a variety of shapes and from a variety of materials. For example, some fibers have more than one type of polymer in distinct longitudinally co-extensive portions of the transverse cross-section and extending along the length of the fiber. Fibers that have two such portions are known as xe2x80x9cbicomponent fibersxe2x80x9d. Bicomponent fibers having one of the portions surrounding or substantially surrounding the other are referred to as having a sheath/core configuration.
Sheath/core bicomponent polyamide fibers are known. U.S. Pat. No. 5,445,884 to Hoyt and Wilson discloses a filament with reduced stainability having a polyamide core and a sheath of a hydrophobic polymer. The weight ratio between the core and sheath is from about 2:1 to about 10:1. If the sheath is very thin, a compatibilizer must be used. Compatibilizers are generally expensive. The compatibilizer can, in some cases, be eliminated by making the sheath relatively thick, i.e., more than 15 wt % of the cross-section. However, if the sheath material is expensive, this also can add significantly to the cost of the fibers.
U.S. Pat. No. 4,075,378 to Anton discloses sheath/core bicomponent polyamide fibers containing a polyamide core and a polyamide sheath. The core polyamide is acid-dyeable while the sheath polyamide is basic-dyeable due to sulfonation.
U.S. Pat. No. 3,679,541 to Davis et al. describes a sheath/core bicomponent filament having soil-release, anti-soil redeposition and antistatic properties through use of a copolyester or copolyamide sheath around a polyamide core.
U.S. Pat. No. 3,645,819 to Fujii et al. discloses polyamide bicomponent fibers for use in tire cords, bowstrings, fishing nets and racket guts.
U.S. Pat. No. 3,616,183 to Brayford discloses polyester sheath/core bicomponent fibers having antistatic and soil-release characteristics.
U.S. Pat. No. 2,989,798 to Bannerman describes sheath/core bicomponent which is said to have improved dyeability by modifying the amine end group level of the sheath relative to the core. The sheath has less amine end groups than the core.
Fibers that are non-round in transverse cross-section are known. For example, U.S. Pat. Nos. 2,939,202 and 2,939,201, both to Holland, describe fibers having a trilobal cross-section.
Polyamide fibers may be dyed to popular colors, usually after being tufted or woven into carpet face fiber. The dyestuffs used to dye the fibers are subject to fading. One mode of fading of dyed yarns is via ozone. This is a particular problem in areas that are near coastlines (i.e., hot and humid) or in homes that have electrostatic dust precipitators. Carpets installed in automobiles are also subject to heat and humidity. Ozone reacts with dyestuffs, especially disperse and cationic dyestuffs, and renders them colorless or off-shade. Acid dyestuffs are also susceptible to ozone fading. Fading is a significant barrier to the sales of uncolored nylon 6 yarn (which is intended to be dyed) into the commercial carpet (contrasted to the residential) market. To achieve acceptable ozone fading resistance in commercial applications, the yarn often must be pigmented during spinning rather than using the more flexible (with respect to color and style) dyeing processes that are performed at the carpet mill rather than upstream at the fiber producer.
Broadly, the present invention relates to dyeable filaments and methods. More specifically, the present invention relates to bath-dyed or dyeable filaments and methods for sheath/core filaments having a core and a sheath which surrounds entirely the core. The core is formed of a core polymer which is susceptible to dyeing by a bath dye chemical, while the sheath is formed of a sheath polymer which is resistant to dyeing by the bath dye chemical. When the filament is brought into contact with a dye bath containing the dye chemical, the dye chemical in the dye bath will be physically transported (that is, will diffuse, migrate or penetrate) through said sheath polymer to cause the core polymer to be dyed a color of the dye chemical, while the sheath polymer is substantially undyed thereby.
These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.